Differentiating implicit and explicit theory of mind and associated neural networks in youth at Clinical High Risk (CHR) for psychosis

Background: Theory of mind (ToM) has been shown to be impaired in Clinical High Risk (CHR) for psychosis populations and is linked to functional outcomes and symptom severity. Implicit versus explicit ToM has seldom been differentiated in this group, and underlying neural networks have also gone unexplored. Methods: 24 CHR and 26 healthy volunteers (HV) completed a behavioral ToM measure called the Short Story Task (SST), as well as a resting state functional MRI scan. SST performance was correlated to attenuated psychosis symptoms. Interactions between group and ToM variables (implicit, explicit, and comprehension) on global efficiency in the Mentalizing (MENT) and Mirror Neuron System (MNS) were also examined. Results: CHR individuals made significantly fewer spontaneous mental state inferences. There were trend-level associations between ToM variables and symptoms, such that greater ToM performance predicted less severe symptoms. There was an interaction of group by spontaneous mental state inference within MENT bilateral dorsomedial prefrontal cortex (dmPFC), such that CHR individuals that made spontaneous mental state inferences showed greater global efficiency within the MENT network's bilateral dmPFC. Discussion: Findings suggest implicit ToM deficits are observable prior to psychotic disorder onset, and that these deficits implicate MENT network dmPFC efficiency. Explicit ToM performance was unaltered in the CHR group, and there were no interactions observed within MNS, suggesting specificity of implicit ToM associations with MENT network dmPFC global efficiency. Results identify potential treatment targets for the neural underpinnings of ToM, thus informing prevention and intervention efforts.